1. Field of the Invention
The present invention relates to a core drill for drilling a fine hole, which is used for drilling a fine hole having a diameter about some tens .mu.m onto a work formed from a metal or a ceramics, or for grinding an inner diameter of the drilled fine hole to a predetermined shape, and a method of manufacturing the same.
For example, a core drill having no spiral groove for discharging chips and grinding powders is used as a tool for drilling a fine hole having a diameter about some tens .mu.m onto the work or for grinding an inner diameter of the fine hole already drilled in accordance with an ultrasonic machining.
2. Description of Related Art
Conventionally, as this kind of core drill for drilling the fine hole, there has been known one structured such that an abrasive grain is fixed to a superfine core material in accordance with a plating treatment by a nickel or a copper after electro-coating a diamond abrasive grain or a ceramics abrasive grain on a surface of the core material such as a piano wire or a cemented carbide tungsten, and a diameter of the drill has been about 50 .mu.m at the minimum.
However, since the diameter is fine, it is hard to uniformly electro-coat the abrasive grain on a periphery of the core material, so that there have been problems such as a plated film fixing the abrasive grain on the core material is easily broken away together with the abrasive grain when an external force is operated, in addition that the abrasive grains partly cohere so as to easily attach.
Further, since the diameter of the core drill is determined by a diameter of the core material and a thickness of the plated film, it is necessary to finely adjust the thickness of the plated film for finishing the diameter of the core drill at a predetermined accuracy, particularly in the case that the diameter of the drill is fine, the adjustment has been hard.
Still further, in the case that the core material is made of a metal material such as a piano wire, since there is a limitation for making the diameter of the core material fine, it is significantly hard to manufacture a core drill having a diameter finer than the current size in the manufacturing method which applying a plating treatment to the core material so as to fix the abrasive grain.